A search engine typically matches a user's query against a collection of target items (e.g., ads, web pages, etc.) by comparing the tokens of the query with the tokens associated with individual target items. The search engine then delivers one or more target items (if any) that have instances of keyword information that most closely match the query, based on any environment-specific matching criteria. In some scenarios, the target items correspond to ads having bidded keyword information associated therewith.
Many times, however, a user fails to enter a query that concisely expresses his or her intent. For example, the query may be relatively verbose and may contain words that are tangent to the user's principal search intent. As a result, the search engine may fail to locate the most relevant target items and present them to the user. The user is thereby disadvantaged because the user may be deluged with potentially irrelevant target items, to varying degrees. The user may also need to extend the length of his or her search session in hopes of finding useful target items. The search engine is disadvantaged because it wastes communication and processing resources in responding to the user in the course of the extended search session. Finally, in an advertising-related context, both advertisers and the entity which administers the search engine are disadvantaged because revenue is lost through the inefficient placement of the target items.